Rare cancers are defined as those with 40,000 cases per year. There are over 130 separate types of primary CNS tumors, all of which meet the definition of a rare cancer. However, some CNS cancers have incidences of less than 1,000 cases per year. Because of its relative rarity, limited reports of the presentation and clinical course have been completed. An additional consequence of the relative rarity of these CNS tumors, studies to evaluate risk factors for the occurrence of these rare CNS tumors or predicting the clinical course of these rare CNS tumors are also limited. Rare CNS tumors like other cancers, occur when there are changes to genes that control the way cells grow and divide often as a result of exposure to other environmental risk factors. Therefore, exploring genetic changes in persons with rare CNS tumors will allow us to begin to understand what changes are associated specifically with these tumors. To date, these participants are often included as part of larger cohorts which include other types of brain tumors. We now understand that even among gliomas, the risk factors differ]. Therefore, identifying the risk factors specifically associated with rare CNS tumors is critical for primary prevention and early detection. This knowledge would allow scientists and physicians to eventually screen for these changes or target the genes or the processes they control for treatment purposes.